<template>
	<view class="u-wrap" :style="[height]">
		<view class="u-menu-wrap">
			<scroll-view scroll-y scroll-with-animation class="u-tab-view menu-scroll-view" :scroll-top="scrollTop" :scroll-into-view="itemId">
				<view
					v-for="(item, index) in category"
					:key="index"
					class="u-tab-item"
					:class="[current == index ? 'u-tab-item-active' : '']"
					@tap.stop="swichMenu(index)"
				>
					<text class="u-line-1">{{ item.name }}</text>
				</view>
			</scroll-view>
			<scroll-view :scroll-top="scrollRightTop" scroll-y scroll-with-animation class="right-box" @scroll="rightScroll">
				<view class="page-view">
					<view class="class-item" :id="'item' + index" v-for="(item, index) in category" :key="index">
						<view class="item-title">
							<text>{{ item.name }}</text>
						</view>
						<view class="item-container" v-if="item.childlist.length">
							<view
								class="thumb-box"
								v-for="(item1, index1) in item.childlist"
								:key="index1"
								@click="goPage('/pages/goods/goods?category_id=' + item1.id)"
							>
								<image class="item-menu-image" :src="item1.image || vuex_config.default_category_img" mode="aspectFill"></image>
								<view class="item-menu-name">{{ item1.name }}</view>
							</view>
						</view>
						<view class="u-p-30" v-else>
							<view class="u-text-center u-tips-color">
								暂无更多分类~~
							</view>
						</view>
					</view>
				</view>
			</scroll-view>
		</view>
	</view>
</template>

<script>
export default {
	name: 'fa-categories',
	props: {
		height: {
			type: Object,
			default() {
				return {};
			}
		}
	},
	mounted() {
		this.current = this.vuex_current;
		this.getCategory();	
		this.getMenuItemTop();
	},
	data() {
		return {
			scrollTop: 0, //tab标题的滚动条位置
			oldScrollTop: 0,
			current: 0, // 预设当前项的值
			menuHeight: 0, // 左边菜单的高度
			menuItemHeight: 0, // 左边菜单item的高度
			itemId: '', // 栏目右边scroll-view用于滚动的id
			category: [],
			menuItemPos: [],
			arr: [],
			scrollRightTop: 0, // 右边栏目scroll-view的滚动条高度
			timer: null // 定时器
		};
	},
	methods:{		
		// 点击左边的栏目切换
		async swichMenu(index) {
			if (this.arr.length == 0) {
				await this.getMenuItemTop();
			}
			this.$u.vuex('vuex_current',index);
			if (index == this.current) return;
			this.scrollRightTop = this.oldScrollTop;
			this.$nextTick(function() {
				this.scrollRightTop = this.arr[index];
				this.current = index;
				this.leftMenuStatus(index);
			});
		},
		// 获取一个目标元素的高度
		getElRect(elClass, dataVal) {
			new Promise((resolve, reject) => {
				const query = uni.createSelectorQuery().in(this);
				query
					.select('.' + elClass)
					.fields(
						{
							size: true
						},
						res => {
							// 如果节点尚未生成，res值为null，循环调用执行
							if (!res) {
								setTimeout(() => {
									this.getElRect(elClass);
								}, 10);
								return;
							}
							this[dataVal] = res.height;
							resolve();
						}
					)
					.exec();
			});
		},
		// 观测元素相交状态
		async observer() {
			this.tabbar.map((val, index) => {
				let observer = uni.createIntersectionObserver(this);
				// 检测右边scroll-view的id为itemxx的元素与right-box的相交状态
				// 如果跟.right-box底部相交，就动态设置左边栏目的活动状态
				observer
					.relativeTo('.right-box', {
						top: 0
					})
					.observe('#item' + index, res => {
						if (res.intersectionRatio > 0) {
							let id = res.id.substring(4);
							this.leftMenuStatus(id);
						}
					});
			});
		},
		// 设置左边菜单的滚动状态
		async leftMenuStatus(index) {			
			if (this.category[index].childlist.length < 10) {
				return;
			}
			this.current = index;
			// 如果为0，意味着尚未初始化
			if (this.menuHeight == 0 || this.menuItemHeight == 0) {
				await this.getElRect('menu-scroll-view', 'menuHeight');
				await this.getElRect('u-tab-item', 'menuItemHeight');
			}
			// 将菜单活动item垂直居中
			this.scrollTop = index * this.menuItemHeight + this.menuItemHeight / 2 - this.menuHeight / 2;
		},
		// 获取右边菜单每个item到顶部的距离
		getMenuItemTop() {
			new Promise(resolve => {
				let selectorQuery = uni.createSelectorQuery().in(this);
				selectorQuery
					.selectAll('.class-item')
					.boundingClientRect(rects => {
						// 如果节点尚未生成，rects值为[](因为用selectAll，所以返回的是数组)，循环调用执行
						if (!rects.length) {
							setTimeout(() => {
								this.getMenuItemTop();
							}, 10);
							return;
						}
						rects.forEach(rect => {
							// 这里减去rects[0].top，是因为第一项顶部可能不是贴到导航栏(比如有个搜索框的情况)
							this.arr.push(rect.top - rects[0].top);
							resolve();
						});
					})
					.exec();
			});
		},
		// 右边菜单滚动
		async rightScroll(e) {			
			this.oldScrollTop = e.detail.scrollTop;
			if (this.arr.length == 0) {
				await this.getMenuItemTop();
			}
			if (this.timer) return;
			if (!this.menuHeight) {
				await this.getElRect('menu-scroll-view', 'menuHeight');
			}
			this.timer = setTimeout(() => {
				// 节流
				this.timer = null;
				// scrollHeight为右边菜单垂直中点位置
				let scrollHeight = e.detail.scrollTop + this.menuHeight / 2;
				for (let i = 0; i < this.arr.length; i++) {
					let height1 = this.arr[i];
					let height2 = this.arr[i + 1];
					// 如果不存在height2，意味着数据循环已经到了最后一个，设置左边菜单为最后一项即可
					if (!height2 || (scrollHeight >= height1 && scrollHeight < height2)) {
						this.leftMenuStatus(i);
						return;
					}
				}
			}, 10);
		},
		getCategory() {
			this.$api.getCategory().then(res => {
				if (res.code == 1) {
					this.category = res.data;
				}
			});
		}
	}
};
</script>

<style lang="scss" scoped>
.u-wrap {
	display: flex;
	flex-direction: column;
}

.u-menu-wrap {
	flex: 1;
	display: flex;
	overflow: hidden;
}

.u-tab-view {
	background: #f6f6f6;
	width: 200rpx;
	height: 100%;
}

.u-tab-item {
	height: 110rpx;
	box-sizing: border-box;
	display: flex;
	align-items: center;
	justify-content: center;
	font-size: 26rpx;
	color: #444;
	font-weight: 400;
	line-height: 1;
}

.u-tab-item-active {
	position: relative;
	color: #000;
	font-size: 30rpx;
	font-weight: 600;
	background: #fff;
}

.u-tab-item-active::before {
	content: '';
	position: absolute;
	border-left: 4px solid #374486;
	height: 32rpx;
	left: 0;
	top: 39rpx;
}

.u-tab-view {
	height: 100%;
}

.right-box {
	background-color: rgb(250, 250, 250);
}

.page-view {	
	// padding: 16rpx;
	.class-item {	
		padding-bottom: 30rpx;
		background-color: #FFFFFF;
		border-radius: 5rpx;
		.item-title {
			font-size: 26rpx;
			color: $u-main-color;
			font-weight: bold;
			padding: 30rpx;	
		}
		.item-container {
			display: flex;
			flex-wrap: wrap;
			
			.item-menu-name {
				margin-top: 15rpx;
				font-weight: normal;
				font-size: 24rpx;
				color: $u-main-color;
			}
			
			
			
			.thumb-box {
				width: 33.333333%;
				display: flex;
				align-items: center;
				justify-content: center;
				flex-direction: column;
				margin-top: 20rpx;
			}
			
			.item-menu-image {
				width: 120rpx;
				height: 120rpx;
				border-radius: 5rpx;
			}
		}
	}
}

.class-item:last-child {
	min-height: 30vh;
}

</style>
